Archive for the ‘General Relativity’ category

There be dragons out there, waaaaay out there, in the dark, off the edge of the map.

Or rather, a virtuoso combination of observation and mathematical modeling has led to an exciting, in some ways joyously old-school prediction. Orbital oddities identified in a handful of distant Kuiper Belt Objects (KBOs) were subjected to the same kind of inquiry that allowed 19th century astronomers to infer Neptune from Uranus’s behavior, in what was widely understood to be a triumph of Isaac Newton’s “System of the World.”

The new analysis, by two Caltech astronomers, theoretician Konstantin Batygin and the observer and Slayer-of-Pluto Michael Brown, has led to a broad outline of what to expect — a ~10 Earth mass planet travelling a very eccentric orbit that never comes closer to the sun than ~250 Earth-Sun distances, a unit of measure known as the Astronomical Unit.

I’m sure many of you saw the news about this last week. Alexandra Witze in Nature had a good write-up, as did Alan Burdick in The New Yorker. (For those (quite a few) on the blog with the urge to read the original Batygin-Brown paper — go here.)

But for all that excitement, there’s something special about a new major planet. As I write in The Hunt for Vulcan[Shameless Plug Here], the idea of a whole new world joining the neighborhood had enormous romantic power in the eighteenth and nineteenth century. Arguably, given our present immersion in the imagined reality of multiple worlds, that romance cuts deeper still today.

But. ButButButButBut….it’s important to remember that a prediction, no matter how well supported, how seemingly necessary, isn’t the same thing as proof, as the discovery itself. That’s what I tried to say in this essay on the subject. A sample:

In 1846, the discovery of Neptune turned Le Verrier into a celebrity; for a time, he was the most famous man of science in the world. He went on an international tour and seized the moment to rise to the top of power in the highly contentious and hierarchical world of French astronomy. Batygin and Brown are taking a much more measured tack with Planet Nine—and for good reason. “We felt quite cautious about making the statement we made,” Batygin says. Why such concern? Because, he says, “immediately after the detection of Neptune spurious claims of planets in outer solar system began to surface. We didn’t want to be another red herring.”

It wasn’t just the distant reaches of the solar system that tripped people up:

…Le Verrier himself was one of the first to be fooled by the impeccable logic of Newton’s theory. After Neptune, he turned his attention to the inner solar system, and he showed (correctly) that Mercury’s orbit wobbles in a way that a Newtonian accounting couldn’t explain. With his own recent triumph so fresh in his—and everyone else’s—mind, the explanation was obvious: There must be a planet hidden in the ferocious glare of the sun, one soon dubbed Vulcan. Within months of making that prediction, Le Verrier trumpeted as a settled discovery an amateur astronomer’s claim to have seen Vulcan crossing the face of the sun. Over the next two decades, at least a dozen other reputable observers reported similar sightings.

The only problem being, of course, that Vulcan was never there.

I’m much more hopeful for Batygin and Brown’s Planet Nine, but hopeful don’t pay the rent — or, as Batygin told me:

“If Newton is right, then I think we’re in pretty good shape,” says Batyagin. “We’re after a real physical effect that needs explanation. The dynamics of our model are persuasive.” And yet, he adds, that’s not enough. “Until Planet Nine is caught on camera it does not count as being real. All we have now is an echo.”

There’s a surfeit of terrestrial crazy to weigh us down. It’s a relief, I find, to look up and out, and contemplate the ordered mysteries that so thoroughly dwarf Comrade Trump’s Yuuuuuggggge self conceit.

Belated happy birthday to the big squid on the block of science blogging — see Bora’s (who else’s?) catalogue of those around the blogosphere who responded in a more timely fashion to the Dear Cephalopod’s numerologically significant planetary rotation.

Not much to add to the universal cheer for PZ Myers continued presence on earth, except a quibble. (What did you expect? This is a blog, for Spagetti Monster’s sake).

PZ, in his acknowledgment of the outpouring of blogolove, noted that his accomplishment was pretty ordinary:

Now I do have to remind you all, though, that we’re all aging at exactly the same rate (unless you have access to a spaceship that travels at a significant fraction of the speed of light), and all I’ve got is a head start on many of you…

But alas, PZ here makes an error common to the non physicist or non-mud-grubbing pedant. (as my last physics course was some 34 years ago, guess which category into which I fall.) He nods towards the special relativistic side of time dilation, but, (horrors!) he ignores the gravitational impact on the passage of time.

The effect is a consequence of the way Albert Einstein’s general theory of relativity. (See here, or here. Fwiw, I wrote and directed the animations accompanying the second essay. They’re more than ten years old, but I still like them). General relativity states that strong gravitational fields make clocks run slower than clocks in a weaker field — as in fact they do. An observer at sea level will, if she happens to have an atomic clock handy, observe time as passing more slowly than will her colleague flying in an atomic-clock equipped airplane. (More precisely — the airborne clock will be observed to have run slightly fast compared to the clock on the ground when the plane lands.)

The effect is small in most circumstances (not near a black hole, though!) — but significant enough to matter a great deal to the Global Positioning System. (Click on Clifford Will to see the relevant essay.) Left uncorrected, the seemingly small time dilation effect (a clock on a satellite in geosynchronous orbit orbiting medium earth orbit altitude used by the GPS system (20,200 kilometers or 12,552 miles) ticks 45 microseconds/day faster than a clock on earth) would, even when accounting for special relativity, which pushes slows the speedy satellites’ clocks by 7 microseconds/day, produce navigation errors of more than 10 kilometers a day. Will writes that failing to account for the effect would render the system useless for navigation in just two minutes.

All of which is to say that PZ, professing reason at about 1,138 ft above sea level, (give or take the height of his office building), is aging slightly slower than any colleague he might want to chaff at the University of Colorado, Boulder, altitude 5,430, but just a smidgeon faster than your faithful blogger, writing this in Boston (ish), maybe a hundred feet above high tide.